1. Field of the Invention
The present invention relates to an injection molding machine in which software is used to determine interruption of power supply to a motor when a safety door is opened.
2. Description of the Related Art
A molding cycle of an injection molding machine comprises a process for closing a mold, process for injecting a molten resin into the mold, process for melting and metering the resin for the next molding cycle, process for opening the mold, and process for ejecting a molded product from the mold. In the process for closing the mold (consisting of movable and stationary mold halves), among these various processes, the mold is rapidly closed under high thrust. Therefore, it is very dangerous if the whole or part of an operator's body gets in between the movable and stationary mold halves while the mold is being closed.
To overcome this, a moving part of the injection molding machine is provided with a safety door for ensuring the safety of the operator who operates the machine. Further, Japanese Patent Application Laid-Open No. 60-262617 discloses a system for ensuring an operator's safety, in which a servomotor is safely stopped by outputting a motor stop signal or motor power interrupt signal to a servo amplifier for driving the servomotor when the safety door is opened.
Moreover, a fail-safe method for improved safety is known as a means for ensuring an operator's safety during a risky process of operation, such as mold opening/closing operation. More specifically, a series of power interruption circuits configured to output motor power interrupt signals to a servomotor is provided in two independent systems. Thus, if any interruption circuit in one of the systems goes wrong, its safety can be ensured by interruption operation of an interruption circuit in the other system. Further, Japanese Patent Application Laid-Open No. 2005-165755 discloses low-cost, high-reliability power interruption circuits of this type configured to mutually monitor their respective operating states.
To ensure the safety of the injection molding machine, power supply to a motor should preferably be interrupted when the safety door is open. In contrast, Japanese Patent Application Laid-Open No. 2002-361703 discloses an injection molding machine which is configured not to interrupt power supply to a motor (to establish a semi-automatic override mode) event when a safety door is open, for convenience, on the condition that ‘additional safety measures’ are taken against some operations, e.g., mold opening operation, molded-product ejecting operation, etc.
Such ‘additional safety measures’ include use of two-hand push buttons and a mechanical safety device for prohibiting mold closing operation, for example. When changing a motor power interruption criterion for determining whether or not to interrupt power supply to the motor when the safety door is opened, depending on the presence or absence of the additional safety measures, a power interruption determining circuit formed of a relay and the like should only be replaced according to presence or absence of the safety measure. However, the replacement of such an electrical circuit is not easy, and a plurality of electrical circuits must be provided in advance, depending on the type of the “additional safety measures”.
If the motor power interruption circuit is formed of software in place of the electrical circuit, on the other hand, it can provide a low-cost advantage. In case where two motor power interruption criteria are included in the same software and either one of the two is used by switching over, however, the reliability of a switching unit must be enhanced not to make start operating with an unintended motor power interruption criterion due to erroneous setting or operation.